Orientation Control of the (alpha_2+gamma) Lamellar Microstructure in TiAl Intermetallic Compounds by Thermo-mechanical Treatment

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A process consisting of the high-temperature deformation in alpha single phase region followed by the annealing and deformation in (alpha_2+gamma) region is examined, in order to control the alignment of the lamellar microstructure with the constituents of alpha_2 and gamma phases in the TiAl based alloys. The uniaxial compression in the alpha single phase region resulted in the formation of a fiber texture, though dynamic recrystallization occurred. The maximum pole density for the compression plane appeared about 35 degrees away from (0001) of the alpha_2 phase. The heat treatment generates the lamellar microstructure reflecting the texture formed by the uniaxial deformation in the alpha single phase region. Work softening was observed at the deformation of the specimen with fully lamellar microstructure formed by the deformation in the alpha single phase region and the annealing in the two phase region. The work softening was attributed to the geometrical softening at the initial stage and dynamic recrystallization in the later stage of deformation. The deformation in the two phase region brought about the rotation of the lamellae. The lamellar interface lied almost parallel to the compression plane after the deformation of about -0.8 in true strain.